The present invention relates generally to a zoom lens, and particularly to a zoom lens designed to cover a medium telephoto zone having a total angle of view of 25° to 35° at the wide-angle end and a zoom ratio of 3 to 5.
More particularly, the invention is concerned with a zoom lens that is suitable for use as an interchangeable lens for single-lens reflex cameras.
So far, the zoom lens set forth in Patent Publication 1 has been known as a zoom lens adapted to cover a medium telephoto zone and lend itself to interchangeable lenses for single-lens reflex cameras. That zoom lens is made up of, in order from its object side, a first lens group of positive refracting power, a second lens group of negative refracting power and a third lens group of positive refracting power, wherein zooming from the wide-angle end to the telephoto end is implemented by varying an axial spacing between the first and the second lens group and an axial spacing between the second; and the third lens group. And, the zoom lens operates in such a moving mode that the total length of the zoom lens becomes short at the wide-angle end.
Patent Publication 1
JP (A) 62-9311
However, problems with this zoom lens are that the second lens group is likely to interfere with the third lens group on the telephoto side; the refracting power of the first lens group is too strong to hold back aberration fluctuations due to changes in the spacing between the first and the second lens group; the first lens group is thick, etc. all working against size reductions and higher zoom ratios.